This invention relates generally to magnetic tape drives, and more particularly to a mechanism for transversely positioning a magnetic tape head relative to the direction of travel of the magnetic tape.
Magnetic tape drives are used extensively as memory backup devices for small and mid-size computer systems. A streaming tape drive stores data in parallel longitudinal tracks on a length of magnetic tape typically 1/4" or 1/2" wide. High speed and recording density are achieved by writing or reading each track as a single stream of data without interruption, thus eliminating inefficiencies due to starting and stopping the tape. At the end of a track the magnetic tape head is moved transversely across the tape to access an adjacent parallel track before the tape direction is reversed and the adjacent track is accessed.
The precision with which the tape head can be positioned across the tape determines the density of the parallel tracks on the tape. The magnetic head must be capable of moving transversely across the tape in increments at least as small as the width of a track, and be accurately maintained at each position. Similarly, the tape head must be repeatably positionable at each track to recover the data on that track. Typically, a leadscrew driven by a stepper motor moves the tape head which is coupled to the threads of the leadscrew so that the head moves a predetermined distance across the tape for each rotation of the leadscrew. Uncontrolled motion of the head relative to the tape produces positioning errors which result in data errors in reading or writing a track. Reducing uncontrolled motion is critical, especially where the tracks are densely packed.